Unless your TV is an HDTV, composite output or S-video is the best resolution you're gonna be able to display at, which really doesn't look good. It's okay enough for watching videos but not of a high enough resolution for actual use as a PC moniter.
If you have a regular TV and only want an S-video connection for watching clips on your TV, buy an entry-level PCIe graphics card. I suggest an X300, as ATI has much better TV-OUT functionality. Many of them have s-video output, and sell for around next to nothing on ebay. It's truly the cheapest route for SDTV.
If you have an HDTV, you could see if your TV currently supports RGBHV component input. It probably won't, but you could look. If not, some ATI models of cards support HD output with the purchase of ATI's component output dongle. Only certain models of ATI cards can do this however, and no, I don't know which PCIe cards can (on the AGP side, the old Radeon 8500 is an excellent choice). I've read that the Nvidia 6600GT also had built-in HD output, so that always a choice. Buying a dedicated graphics card is the cheapest route to HD resolutions from your computer. The only other alternative is to purchase a transcoder that converts your RGBHV signal from your VGA's D-SUB into a usable traditional YUV output for your HDTV, but those cost around $200. Actually, if you had a digital HDTV (ie most quality LCD HDTV displays are digital, and all CRT-based HDTVs are analog) the best route would be to use a graphics cards with DVI output and then purchase a DVI to HDMI adapter, thereby sending a pure digital signal to your digital HDTV (no digital to analog to digital conversion necessary=better picture). The VGA D-SUBs are analog.